1. Field of the Invention
The present invention relates to a circuit breaker such as no-fuse circuit breakers or earth leakage breakers and, more particularly, to a circuit breaker of which specification can be easily changed depending on breaking capacity.
2. Description of the Related Art
A circuit breaker not only has the function of make-and-break of an electric circuit, i.e., the switch function by the operation of an operating handle provided at this circuit breaker, but also has the function of breaking an electric circuit for preventing electric wires or current consumers from burning due to the flow of an over-current, i.e., an important role of breaking function. This breaking of an electric circuit is defined to be within a range of 1 kA to 200 kA as “rated breaking current” in accordance with, for example, JIS (Japanese Industrial Standard) C8370. It is as known that each manufacturer intends to provide a wide range of product variations so as to select a circuit breaker having a suitable rated breaking current depending on situations of the electric circuit, that is, distance from a transformer, or thickness of an electric wire.
At the time of breaking an electric circuit in such a circuit breaker, molten metallic materials or molten insulating materials due to the generation of arc heat may be scattered in the surrounding area along with arc gas, and the molten materials may be adhered to the make-and-break mechanism or the trip mechanism. In general, a circuit breaker is capable of interrupting a rated breaking current about two to three times. Further, when considering that the rapid reset operation (sliding shift to the OFF position of an operating handle) is made, for example, to stop an alarm output having been generated at the time of breaking, it is not desirable that functions of the above-mentioned make-and-break mechanism or trip mechanism are impaired due to adhesion of the above-mentioned molten materials.
To address such problems, conventionally, as shown in the Japanese Patent Publication (unexamined) No. 228669/2005, the following circuit breaker is proposed. This circuit breaker is arranged such that an insulating housing of the circuit breaker is divided into a case body, a middle cover to be mounted on the top of this case body, and a top cover with which the top of the middle cover is covered; a contact portion where arc is generated and an arc-extinguishing device functioning to extinguish this arc, are contained in the case body; and a make-and-break mechanism or a trip mechanism is contained in the middle cover to separate the above-mentioned make-and-break mechanism or trip mechanism from the contact portion, thereby preventing the adhesion of molten materials to, e.g., make-and-break mechanism.
However, in the circuit breaker as shown in the above-mentioned Japanese Patent Publication (unexamined) No. 228669/2005, due to the fact that a partition wall over each of the poles is formed at the bottom of the middle cover and a make-and-break mechanism or a trip mechanism is attached to a central pole portion of the above-mentioned partition wall, a middle cover will be inevitably an indispensable part to construct a circuit breaker. Since there are varieties of rated breaking currents respectively serving as indexes of performance capability of a circuit breaker as described above, there is no reason that a circuit breaker should have a large rated breaking current. Rather, it is preferable to select a rated breaking current in light of situations of an electric circuit thereof.
Nevertheless, in the case of a comparatively small rated breaking current, the adhesion of molten materials is not regarded as a disadvantage, so that the mounting of a middle cover is an over specification, and there will be the possibility of being less cost competitive.
Furthermore, in the case of preparing a circuit breaker without the use of the middle cover in order to prevent the over specification, it is necessary to review the entire construction of a make-and-break mechanism itself. Thus, a problem exists in that it is difficult to share parts depending on the magnitude of rated breaking current, that is, the difference in breaking capacity.